<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        div {
            background-color: red;
            height: 200px;
            width: 200px;
        }
        #r10px {
            border-radius: 10px;
        }
        #r50px {
            /* border-radius: 50px; */
            border-radius: 50%;
        }
    </style>
</head>
<body>
    <h2>没有设置圆角</h2>
    <div></div>
    <h2>圆角10px</h2>
    <div id="r10px"></div>
    <h2>圆形</h2>
    <div id="r50px"></div>
</body>
</html>